1. Field of the Application
The present application concerns an axial turbomachine compressor drum, more specifically a drum equipped with a plurality of rows of vanes, each row, together with a row of vanes of the stator directly downstream from said row, forming one stage of the compressor.
2. Description of Related Art
It is known, for example from patent GB 776,618, to attach the vanes of an axial compressor to its drum by mechanical assembly. Each of the vanes comprises a root having a shape suitable for engaging in abutment with a groove provided on the drum. Typically, the vane root, having two projecting edges forming a hook, is inserted in a circular groove of the drum serving as housing for the vane roots and the vane is then turned along its main axis in such a way that the two edges projecting from the root enter into so-called positive contact, i.e. in abutment, with the two edges of the groove of the drum. Various means of locking the vane in this position are provided in this document, such as screwing means at the root of the vane, screwing means at the drum, sliding lug means on the vane root, under pressure of a spring and capable of engaging with the elements of the drum, or conical shims and counter-shims between the root and the two edges of the groove, said shims and counter-shims being held in place by welding. This technique of attaching vanes to a compressor drum has the disadvantage of requiring a significant mass of material at the vane root as well as at the groove. Indeed, the vanes of the rotor of a compressor are subject to considerable centrifugal as well as other forces. These stresses require a strong attachment of the vanes to the drum. To that end, the roots of the vanes, in particular the hook-forming projecting parts, as well as the edges of the circumferential groove of the drum with which the root of the vane engages, are dimensioned to be rather large. This mass of material at the periphery of the drum causes large centrifugal stresses that the drum must be able to absorb. These excess centrifugal forces to be absorbed require a larger dimensioning of the drum and thus greater weight and higher cost.
A lighter construction of a compressor drum is known from the patent RU 2,270,937 C1. The shell of the drum is constructed by an assembly of rings or spacers connected to each other by rows of vane platforms. The rows of vane platforms form the extension of the shell of the drum. These platforms are welded to each other and to intermediate sections of the shell. However, this construction lacks rigidity and requires numerous reinforcements from the center of the drum to the inner face of the shell, either directly beneath the vanes or beneath the intermediate sections of the shell. This construction proves to be complex, requiring much time to assemble. Production costs are therefore relatively high.
Patent application EP 1319842 A1 discloses a drum in several parts or sections along the axis of rotation and assembled by screwing. The vanes are attached therein at the junctions between the sections, either by interlocking, or directly by screwing means. Indeed, in the first case, the vane roots have a shape with edges projecting approximately along the direction of the axis of rotation, said projecting edges engaging with corresponding grooves on each section end at the junction thereof. During the assembly of two sections, the vane roots, in particular the projecting edges thereof, are confined in the opposite grooves of the sections and are placed under pressure when the attaching means are tightened. In the second case, the vane roots include bores through which the means of attaching the sections are assembled. This construction of the drum or rotor in several sections or rings poses problems of precision during assembly. Moreover, the parts of sections engaging with the vane roots and also with the attachment means must be dimensioned rather large in size in order to be able to absorb the centrifugal forces on the vanes, as well as the occasional stresses from tightening them.
Although great strides have been made in the area of axial turbomachine compressor drums, many shortcomings remain.